The present invention relates to the production of 1,2-diphenylethylene (stilbene) and derivatives thereof.
Stilbene, because of its unsaturated character, is very reactive and may be employed in various organic syntheses. It is useful in the production of products which may be used in the manufacture of dyes, paints and resins. It is also useful in optical brighteners, in pharmaceuticals and as an organic intermediate.
Heretofore, stilbene has not been available in commercial quantities because the attendant yields of the known processes for the manufacture of stilbene have been generally small. Stilbene has been synthesized by dehydrogenation of bibenzyl; by dehydrogenation of 1,2-bis(3-cyclohexen-1-yl)ethylene (U.S. Pat. No. 3,387,050); and by reacting a benzyl mercaptan with a sulfactive catalyst, for example, molybdenum disulfide and copper sulfide (U.S. Pat. No. 2,645,671). Stilbene and halostilbenes have been synthesized by the iodative dehydrocoupling of toluene and halogen-substituted toluenes with elemental iodine and molten lithium iodide at toluene conversions of 10-30% (U.S. Pat. No. 3,409,680). In U.S. Pat. No. 3,205,280, a catalytic dehydrogenation process is disclosed wherein certain hydrocarbons are converted to less saturated hydrocarbons by heating a mixture of hydrocarbon with at least 0.001 mol of a halogen per mol of hydrocarbon in the presence of free oxygen and a solid catalyst of an alkali metal halide and silver halide and additionally oxides and halides of certain elements.
In U.S. Pat. No. 3,694,518, a dehydrocoupling process is disclosed wherein toluene is converted to stilbene by heating toluene with oxygen in the presence of iodine and, optionally, an inert heat carrier material. In U.S. Pat. No. 3,868,427 this process of dehydrocoupling is carried out in the presence of a metal oxide, preferably palladium oxide coated on alpha-alumina.
Dehydrocoupling of toluene by the reaction with lead oxide to form stilbene has been reported by Behr and Van Dorp, Chem. Ber. 6,753 (1873) and Lorenz, Chem. Ber. 7,1096 (1874). In this reported work, stilbene is obtained by conveying toluene over lead oxide maintained at or about at a dark red glow. More recent disclosures of the metal oxide-toluene reaction are given in U.S. Pat. No. 3,476,747 and U.S. Pat. No. 3,494,956. The former patent relates to preparation of 1,2-bis(aryl)ethylenes by contacting of an aryl methane such as toluene with an inorganic oxidant from the group of arsenic pentoxide, antimony pentoxide, bismuth trioxide, manganese arsenate, or antimony tetraoxide at elevated temperatures. In Example 9 of U.S. Pat. No. 3,494,956, it is reported that a mixture of toluene and oxygen passed over heated lead oxide produces bibenzyl. In another patent, U.S. Pat. No. 3,557,235, it is reported that toluene can be oxidatively coupled in a stoichiometric reaction where a metal oxide, such as lead oxide, serves as a source of oxygen in the reaction.